A subsea well may be provided with a tubing hanger for suspending production tubing extending into a reservoir or a dummy reservoir. The tubing hanger may also house a connector that terminates a cable extending downhole to supply power to electrical equipment such as an electric submersible pump located in the reservoir or dummy reservoir. Such connectors in the tubing hanger are subjected to hostile conditions such as extreme temperatures and pressures and aggressive chemicals and thus the connectors need to be designed to deal with these conditions.
A known system for this environment is the SpecTRON 5 (trademark) Electrical Submersible Pump (ESP) power feedthrough system produced by Tronic Limited. This system includes a connector for terminating the cable extending downhole. The termination between the cable and a pin is formed by a cable crimp between the two parts. The termination is covered by an elastomeric termination sleeve stretched over the end of the cable and connector pin. This termination is housed in a cable termination chamber sealed from the downhole environment by an elastomeric diaphragm and an elastomeric cable boot. The elastomeric diaphragm is filled with a dielectric gel. The diaphragm is flexible and may transmit pressure from the ambient environment to the connector internals to maintain a minimal pressure differential.
A first aspect is concerned with providing a downhole termination apparatus with an improved sealing arrangement between a termination of a cable and the downhole environment.
Viewed from a first aspect, in a first alternative thereof, there is provided a downhole cable termination apparatus for terminating a cable that is to extend downhole from a tubing hanger to electrical equipment, the apparatus including: an electrical contact for electrical engagement with a conductor of the cable to form a termination, which, in use, is to be electrically insulated by an insulating portion around the termination; and a seal to be located downhole from the insulating portion for sealing between the insulating portion and the downhole environment, wherein the seal is a metallic seal.
By providing an apparatus with a metallic seal to be provided downhole from the insulating portion, a path between the downhole environment and the insulating portion may be sealed by the metallic seal.
As mentioned above, the connectors in the tubing hanger are subjected to hostile conditions such as extreme temperatures and pressures and aggressive chemicals. Additionally, gases from the well rise up and sit around the connector and elastomers are prone to absorbing these gases.
The pressure in the downhole environment may fluctuate, for example, due to the operation of an electric submersible pump in the well. This pressure fluctuation may cause a problem for the elastomers having absorbed gas. A rapid drop in pressure results in the gas having permeated the elastomer rapidly expanding. The majority of the expanding gas may be absorbed into the material is unable to diffuse to accommodate the expansion and as a result the gas expansion within the material may damage and tear the material. This effect is known as rapid gas decompression (RGD).
In some prior art systems, there have been attempts to minimize the effect of rapid gas decompression by using elastomers that absorb less gas and/or by constraining the elastomers so as to prevent the gas/elastomer volume from expanding and hence preventing the elastomer from tearing. The internal pressure of the constrained elastomer will build up until the gas may diffuse out.